how to make a map<CLSID, string>?

Question

I want to create a container which can associate a CLSID structure to something else (for example, a string); for example, std::map.

(the CLSID means standard Windows CLSID structure)

However when I want to use its find() and insert (object[clsid] = string), the STL just failed and gives errors.

Does anyone know how to solve this?

For example:

typedef std::map<CLSID, std::string> MyCLSIDMap;
MyCLSIDMap mymap;
CLSID sample = CLSID_NULL;

mymap[sample] = string("test");   // compilation failed here

Answer 1

Does your CLSID structure support a usable operator<()? That's crucial for std::map (you can build it as a separate bool functor taking two const CLSID& arguments, it doesn't have to be a method operator<() in CLSID -- but then you'll have to say std::map and not just map ...!).

Answer 2

As Alex has answered, std::map needs to compare it's keys with op<.

bool operator<(CLSID const& l, CLSID const& r)
{
    return memcmp(&l, &r, sizeof(CLSID)) < 0;
}

Answer 3

To use an STL map where the keys are structures, you'll need to provide your own strict weak ordering function object:

struct CompareCLSID
{
  bool operator()(const CLSID &s1, const CLSID &s2) const
  {
    // returns true if s1 is less than s2
  }
};

and then your map's type would be map<CLSID, string, CompareCLSID>.

However, if you don't need your container is sorted (that's my guess), you should be using hash<> or hash_map<>. In that case, you'll have to provide your own hash function.